In recent years, a backlight for a liquid crystal display device equipped with a sidelight composed of numbers of arrayed LEDs is known. In the backlight for the liquid crystal display device, light from LEDs is introduced from an end surface of a light guide plate, scattered, diffused inside the light guide plate and is emitted from a light emitting surface toward a liquid crystal panel.
The backlight for a liquid crystal display device with a structure described, however, had a problem that bright and dark lines appear on the light emitting surface in the vicinity of the end surface of the light guide plate. The reasons are described below. First, it is difficult to suppress the bright lines because the LED is a point light source with strong directional characteristics and strong brightness. Second, it is also difficult to suppress the dark lines due to spaces between point light sources of LED elements, from which no light is emitted. Thus, unevenness in the light emitting surface such as the bright and dark lines are generated in the light guide plate near the sidelight owing to a great contrast difference in the sidelight provided by the numbers of LEDs.
As a measure for eliminating bright lines generated in the light emitting surface of the light guide plate of the backlight having such construction mentioned above, Japanese Unexamined Patent Application Publication No. 2002-175713 discloses a technique in which a plurality of holes are provided at a portion near the sidelight of the light guide plate and a light path is changed by the difference of refraction indexes between the light guide and inside the hole. Further, Japanese Unexamined Patent Application Publication No. 2004-213025 discloses a technique in which a light diffusion member is provided at a position where the light from a source is introduced into a light guide plate, to diffuse the light by a reflection surface before it enters into the light guide plate. However, any of these technologies could not fully eliminate the unevenness of bright and dark lines generated at a portion of light emitting plate near the point light source.